Potential and problems with high‐dose strategies for pesticidal engineered crops

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Abstract
We lack an empirical basis on which to judge the expected durability of crops that express one or more insecticidal proteins and must therefore rely upon theoretical population genetic models in assessing how best to delay pest adaptation to these toxins. A number of studies using such models indicate that expression of toxins at very high levels could slow pest adaptation to a crawl if the ecology and genetics of the pest and cropping system fit specific assumptions. These assumptions relate to: (1) inheritance of resistance factors; (2) ecological costs of resistance factors; (3) behavioral response of larvae and adults to the toxins; (4) plant‐to‐plant movement of larvae; (5) adult dispersal and mating behavior; and (6) distribution of host plants that do and do not produce the toxin(s). This paper includes a discussion of whether the biology of insect pests of a number of cropping systems that are targets for toxin‐expressing plants fit assumptions that are conducive to slowing pest adaptation. Emphasis is placed upon new data regarding the behavior and movement of larvae and the mating structure of populations. New theoretical work that examines the importance of natural enemy mortality and fitness costs of resistance is presented. This paper also discusses how the complexity of developing resistance management strategies increases when multiple pests and multiple crops are considered. Finally, the problems associated with developing resistance management strategies in poor and developing countries are described.